With all due respect, I have very successfully used rattle can paint on my frames and engine cases. I have used it as touchup as well as when doing frame up restorations.
If you apply a good enamel over a properly prepped surface it will last as long as any fancy high end paint, and have the added benefit in that is much easier to repair physical damage.
Proper prep involves degreasing, rust removal, application of rust converter and a self etching primer and final application of several light coats of finish. If you are really concerned about solvent resistance, use an automotive satin finish engine or frame enamel.
As I mentioned in replying to you in another forum, I have used basic hardware store rattle can enamel with great success. Going to special 2k formulas gets you into the realm of diminishing returns and much greater expense.
DSCN2815.JPG (59.65 kB . 768x504 - viewed 50 times) DSCN2782.JPG (65.93 kB . 767x576 - viewed 49 times) DSCN2810.JPG (48.1 kB . 768x412 - viewed 49 times)